1. Field of the Invention
The present invention relates to a vibration-damping device and, more particularly, to an improvement in the structure of a cylindrical vibration-damping device wherein a vibration-damping rubber body having a liquid chamber is disposed between an outer cylinder and an inner cylinder.
2. Description of the Prior Art
FIGS. 5 and 6 illustrate one example of a conventional cylindrical vibration-damping device. In the drawings, a holder 5 secured to a frame of a vehicle has a cylindrical holder portion 51 and a leg portion 52 which supports the cylindrical holder portion 51. A thin-walled outer cylinder 1 is press-fitted into the cylindrical holder portion 51. A vibration-damping rubber body 3 is disposed within the outer cylinder 1.
An internal ring 6 is secured to the outer surface of the vibration-damping rubber body 3 in sealing engagement with the outer cylinder 1. The vibration-damping rubber body 3 defines a space in its lower half portion, which space serves as a main liquid chamber A. A resin block 31 having a size slightly smaller than that of the main liquid chamber A and having a configuration similar thereto is disposed within the main liquid chamber A. An inner cylinder 2 is embedded within the vibration-damping rubber body 3 so as to axially penetrate it. A buffer rubber plate 32 is disposed within another space formed in the upper portion of the vibration-damping rubber body 3 under the internal ring 6 and over the inner cylinder 2. One end of the buffer rubber plate 32 is secured to a facing end of the inner cylinder 2.
The axially central portion of the internal ring 6 caves inwardly. This caved portion opens at a position facing the main liquid chamber A. A ring-shaped throttling member 7 is disposed between the caved portion of the internal ring 6 and the outer cylinder 1. This throttling member 7 opens at its upper portion, and a thin rubber wall 4 is disposed with its peripheral edge fitted between an opening edge of the throttling member 7 and the inner surface of the outer cylinder 1, thereby defining a space between the thin rubber wall 4 and the outer cylinder 1.
The throttling member 7 has parallel channels 71, 72, each facing the outer cylinder 1. One end of the channel 71 communicates with the main liquid chamber A while the other end thereof communicates with the other channel 72. The channel 72 extending in parallel with the channel 71, turns at the point where the parallel channels 71, 72 communicate with each other, and extends to the auxiliary liquid chamber B formed between the rubber wall 4 and the internal ring 6. These parallel channels 71, 72 compose a throttled passageway F.
A bolt connected to an engine is inserted into the inner cylinder 2. When vibrations of the engine are input, the inner cylinder 2 relatively moves with respect to the outer cylinder 1, thereby deforming the shape of the main liquid chamber A. This results in a damping liquid enclosed in the main liquid chamber A flowing into the auxiliary liquid chamber B through the throttled passageway F with a high resistance, and accordingly effective vibration-damping operation being performed.
When vibrations of a too high frequency are input, the inner cylinder 2 abuts on the resin block 31 or the buffer rubber plate 32, thereby preventing the vibration-damping rubber body 3 from excessively deforming.
In order to make a sufficient amount of the enclosed damping liquid flow from the main liquid chamber A to the auxiliary liquid chamber B through the throttled passageway F, the rubber wall 4 defining the auxiliary liquid chamber B is required to freely deform, and the space C is required to have such a sufficient volume as to allow the free deformation of the rubber wall 4.
However, if the volume of the space C is increased in the device of the above-described prior art, there occurs a problem that the overall size of the device becomes too large.
In order to solve this problem, another device as shown in FIGS. 7 and 8 has been proposed. In this device, through holes 55 of a diameter larger than that of the through holes 11 formed in the outer cylinder 1 are provided in the holder portion 51 of the holder 5 so as to communicate with the through holes 11.
In accordance with this device, the thin rubber wall 4 can freely deform because the space C communicates with the atmosphere by way of the through holes 11, 55. However, in order to bring the through holes 1, 55 in communication with each other, precise adjustment of the rotating posture of the outer cylinder 1 with respect to the holder portion 51 is needed. This precise adjustment takes much time and labor.
When the through holes 55 are provided at the upper portion of the holder portion 51, as shown in FIGS. 7, 8, water is likely to stay therewithin, whereby the through holes 55 tend to rust. In order to prevent this problem, covers or like means must be provided in the holder 5.